In semiconductor integrated circuit manufacturing processes, a photoresist layer is often formed on a semiconductor substrate and photolithography is used to define regions for etching or ion implantation. The photoresist layer is removed after the etching or ion implantation processes are completed.
In an existing photolithography technology, the photoresist layer is usually formed in a coating apparatus. To form a photoresist layer, a wafer is transported to the coating apparatus, and a layer of photoresist is spin coated on the surface of the wafer. The wafer with the spin-on photoresist layer is transported to a thermal treatment chamber or a hot plate for thermal treatment or soft bake process to evaporate some of the solvent in the photoresist layer. Then the wafer is transported to a cooling plate to cool down after the thermal treatment.
An existing thermal treatment chamber or hotplate is shown in FIG. 1. The thermal treatment chamber includes a wafer holder 100, a heat reservoir 101 in the wafer holder, temperature sensing units 102 embedded in the wafer holder 100, and an exhaust unit 104 above the wafer holder 100.
The wafer holder 100 may be configured to hold a wafer 103 for the thermal treatment. The heat reservoir 101 may be configured to provide thermal treatment for the wafer holder 100. The temperature sensing units 102 may be configured to detect surface temperature of the wafer holder 100. The exhaust unit 104 may be configured to vent waste gas in the thermal treatment chamber.
Before the wafer is thermally treated, the temperature of the thermal treatment chamber (e.g., the wafer holder) needs to be set to a determined value. However, due to the differences in fabrication processes and product types, the requirement to treat one specific type of photoresist layer or a photoresist layer with a specific thickness is different from another. Thus, the thermal treatment temperature for treating different types of photoresist on a wafer varies accordingly. That is, the thermal treatment temperature in the chamber needs to be adjusted for photoresist of different fabrication processes and product types. When there is a difference between the set temperature value and the real-time temperature, a temperature adjustment is needed to increase/decrease the real-time temperature for it to match the set temperature value.
However, in existing thermal treatment chambers, the time to increase or decrease the chamber temperature may often be too long or it may be difficult to control the chamber temperature.